Here you find the maximum concentricity deviation that Rohm gives for its drill chucks, **LINK**

Niko.

Whichever chuck you have will only be as good as the arbor it's mounted on, sometimes I think the arbor is the cause of runout some people experience.

Emgee

It depends on the accuracy required of the hole!

From the video it looks as if the 0.4mm run-out chuck is too far out, but even so it would still be reasonably accurate at the cutting end if started by a centre-pop, and the hole wasn't too deep (less than a diameter). The reason is drills tend to cut around the spinning axis at the tip and the spring of the drill takes up much of the chuck wobble. A wobbly chuck would be good enough for most woodwork, but probably annoying drilling metal.

A few other points:

• Three jaw chucks, even expensive ones, aren't noted for high-accuracy. Collets are much better.
• Twist drills aren't good either! The shank may not be round, or be bent. Drills won't cut straight unless the cutting edges are ground equally : symmetric angles, lengths, and sharpness. Twist drills can wander if not perfectly perpendicular, if swarf gets in the way, they hit a hard or soft spot, or the lubrication is uneven. Under cutting pressure, the flutes open up, which will cause wandering if one flute is slightly stiffer or weaker than the others. Twist-drills cut straighter if the work rotates rather than the drill – a lathe does better than a mill.

I find twist-drills pretty good for ordinary purposes, but it pays not to rely on them for real accuracy, especially on deep holes. Designs usually adapt to twist-drill short-comings, for example, it's usual for bolt holes to be drilled oversize to leave the bolts room to align with whatever is underneath without binding. Common to see a few bolt holes in a group to be slotted to give even more room.

Accuracy is improved by reaming or boring out drilled holes. Reaming corrects diameter errors, but not bending. Boring fixes both and is the best way of making high-accuracy holes.

I feel it's unwise to chase high accuracy unless specifically needed because ±0.02mm / 1 thou is fairly easily achieved with ordinary tools and methods and is plenty good enough for most jobs. Doing better is hard, needing close attention to technique and better tooling throughout. Might find:

1. Moderately priced twist-drills aren't good-enough, must buy £best
2. £best twist-drills don't perform well in a moderately priced drill chuck, so buy a £best chuck
3. £best chucks don't perform well in a value for money milling machine, so upgrade that as well.
4. And so on. If high-accuracy holes are essential, then the answer might be a Jig Borer, not a milling machine. Not an elderly worn jig-borer either, but one is good condition that's been set-up correctly.

The danger of chasing accuracy for it's own sake is of the whole workshop turning into a tool-room, which is great for accuracy, but dreadful for productivity. Not good if making or repairing typical mechanical engineering stuff is the goal. No problem if achieving ultra-accuracy is the hobby interest, but don't end up buying a tool-room by accident!

Dave

That's why I use collet chuck only on my mill ….

If you are coordinate drilling on your mill then it gets important. You should make a high accuracy holder, not collet blah blah system to hold a spotting drill dead true.

The old fashioned system of marking out on a surface plate, centre popping by feel at the intersection of the microgrooved lines produced, then drilling in stages could get things as accurate as your height gauge. (and skill). A wobbly chuck mattered less, within reason. It also makes sense to have a small chuck for a small drill to start things off. edit – by which I mean a 0-1/4" not a 0-3/8"

Edited By Bazyle on 22/03/2022 13:50:17

We do need to return anything which isn't 'fit for purpose' even if it is cheap or now not so cheap. A lot of things from the east has now gone up by a fair amount, I suppose they will keep pushing until it's as cheap to make it here.

Tony

Collets are probably better than turning your own holders because manufacturers have better kit and Quality Assurance than we do! Unless you go too cheap or get a defective one.

Collets usually have excellent concentricity but only a tiny grip range. In many systems you need a 6mm collet for a 6mm drill, and the number of collets needed to cover all the common imperial and metric sizes is scary.

Good news! A relatively new collet system, ER, has collets that squeeze down a full millimetre much reducing the number of collets needed. The picture below is from ArcEuroTrade, other suppliers available. There's a collet chuck which plugs into the mill (be sure to get the right taper for the machine R8, MT etc), and then a set of individual collets. The most popular hobby size is ER32, covering 1mm to 20mm. ER40 does larger sizes, ER25 smaller. ER collets are used to hold drills and milling cutters (including threaded shanks), plus wobblers, in a mill, and are also suitable for holding work accurately in a lathe. (For which another chuck may be needed.) Have a look at Warco's offerings for prices and what's available.

When buying collet chucks, prefer the type with ball-bearing nuts which are easier to tighten than the plain type. (They like to be tight!) Ball bearing nuts can be bought separately and retrofitted.

I only fit a drill chuck to my mill when drilling lots of different sized holes all in one session, which is rate. The drill chuck allows faster tool changing, which is worth it when drills are being constantly swapped. Otherwise collets are somewhat slower but you get lower run-out and much better resetability.

ArcEuro sell Stevenson Collet Blocks, which are a handy work-holding accessory, if you already have ER:

Dave

You could rule out any mounting error by clamping the drill chuck onto a piece turned/held in the lathe and then clock the drill chuck mounting hole. I have that same chuck as Dan showed and the runout is nowhere near as bad. Factory rejects are getting put into regular circulation.

Mike

To make the collets even more worthwhile, get hex and square collet blocks too. Far better value than the indispensable 123 blocks that I've never found a use for.

For comparison, I had a check of my new Sieg 3.5. This is the first time I use the drill chuck (which was supplied with machine as part of the standard package).

If I measure runout on a quality hss 10mm endmill held in 3 jaw chuck, I get in the region of .25mm runout. Not what I hoped for at all as it is clearly visible and not what I'm used to. Disappointing if I'm using 1mm drills, which was my intention. Any tips on how to get a chuck off a J6 taper so I can compare with other chucks I have? I suspect the R8 adaptor makes a significant contribution as it is not the same quality of finish as that of the separate 10mm collet I got at the same time.

Runout on the same 10mm end-mill in a R8 collet is difficult to measure – I think the movement on my .01mm indicator is due to lack of stiffness in the mill. So I would guess .01 or less. The collet is std from Arc – not std with the Sieg. Does any of this matter if the mill isn't that stiff? Applying hand pressure (maybe 5-7kg) to the head in x directon, with all axis gibs locked, gives .4mm deflection. Much more than I would have guessed.

I got no idea if any of that is good or bad. Not a clue, but I would be much happier if I hadn't measured it Can someone cheer me up?

Edited By jaCK Hobson on 23/03/2022 12:54:11